And what about the OS? Is your server operating system optimal for running a large, high-volume web server? Of course, different operating systems have very different design goals. OpenBSD, for example, is aimed at security, so many of the limits in the kernel are set small to prevent various forms of denial-of-service attacks (one of OpenBSD’s mottoes is “Secure by default”). These limits will most likely need to be increased to run a busy web server.
Linux, on the other hand, aims to be easy to use, so it comes with the limits set higher. The BSD kernels come out of the box with a “generic” kernel, that is, most of the drivers are statically linked in. This makes it easier to get started, but if you’re building a custom kernel to raise some of those limits, you might as well rip out unneeded devices. Linux kernels have most of the drivers dynamically loaded. On the other hand, memory itself is getting cheaper, so the reasoning that led to loadable device drivers is less important. What is important is to have lots and lots of memory and to make a lot of it available to the server.
Memory is cheap these days, but don’t buy cheap memory—brand name memory costs only a little more and repays the cost in reliability.
If you run any variant of Microsoft Windows, be sure you have the server version (e.g., Windows Vista Server instead of just Windows Vista Pro). In other nonserver versions, the end user license agreement and/or the operating system’s code itself may restrict the number of users, or the number of network connections that you can use, or place other restrictions on what you can run. Additionally, be sure you obtain the latest Microsoft service packs frequently, for the obvious security reasons (this is true for any system, but is particularly important for Windows).
This section details a specific set of techniques that will help your Tomcat instance run faster, regardless of the operating system or JVM you are using. In many cases, you may not have control of the OS or JVM on the machine you are deploying to. In those situations, you should still make recommendations in line with what was detailed in the last section; however, you still should be able to affect changes in Tomcat itself. Here is where we think are the best places to start internally tuning Tomcat.